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Movements, leaders, victories and the continuing fight for equality.
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Katherine Johnson’s mathematical calculations helped guide some of America’s most important early space missions while she confronted the racial and gender barriers faced by Black women in twentieth-century America.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
The NX bit (no-execute bit) is a processor feature that separates areas of a virtual address space (the memory layout a program uses) into sections for storing data or program instructions. An operating system supporting the NX bit can mark certain areas of the virtual address space as non-executable, preventing the processor from running any code stored there. This technique, known as executable-space protection or Write XOR Execute, protects computers from malicious software that attempts to insert harmful code into another program’s data storage area and execute it, such as in a buffer overflow attack.
The term "NX bit" was introduced by Advanced Micro Devices (AMD) as a marketing term. Intel markets this feature as the XD bit (execute disable), while the MIPS architecture refers to it as the XI bit (execute inhibit). In the ARM architecture, introduced in ARMv6, it is known as XN (execute never).[1] The term NX bit is often used broadly to describe similar executable-space protection technologies in other processors.
x86 processors, since the 80286, included a similar capability implemented at the segment level. However, almost all operating systems for the 80386 and later x86 processors implement the flat memory model, so they cannot use this capability. There was no "Executable" flag in the page table entry (page descriptor) in those processors to make this capability available to operating systems using the flat memory model, until AMD added a "no-execute" or NX bit to the page table entry in its AMD64 architecture, providing a mechanism that can control execution per page rather than per whole segment.
Intel implemented a similar feature in its Itanium (Merced) processor—having IA-64 architecture—in 2001, but did not bring it to the more popular x86 processor families (Pentium, Celeron, Xeon, etc.). In the x86 architecture it was first implemented by AMD, as the NX bit, for use by its AMD64 line of processors, such as the Athlon 64 and Opteron.[2]
After AMD's decision to include this functionality in its AMD64 instruction set, Intel implemented the similar XD bit feature in x86 processors beginning with the Pentium 4 processors based on later iterations of the Prescott core.[3] The NX bit specifically refers to bit number 63 (i.e. the most significant bit) of a 64-bit entry in the page table. If this bit is set to 0, then code can be executed from that page; if set to 1, code cannot be executed from that page, and anything residing there is assumed to be data. It is only available with the long mode (64-bit mode) or legacy Physical Address Extension (PAE) page-table formats, but not x86's original 32-bit page table format because page table entries in that format lack the 64th bit used to disable and enable execution.
Windows XP SP2 and later support Data Execution Prevention (DEP).
In ARMv6, a new page table entry format was introduced; it includes an "execute never" bit.[1] For ARMv8-A, VMSAv8-64 block and page descriptors, and VMSAv8-32 long-descriptor block and page descriptors, for stage 1 translations have "execute never" bits for both privileged and unprivileged modes, and block and page descriptors for stage 2 translations have a single "execute never" bit (two bits due to ARMv8.2-TTS2UXN feature); VMSAv8-32 short-descriptor translation table descriptors at level 1 have "execute never" bits for both privileged and unprivileged mode and at level 2 have a single "execute never" bit.[4]
As of the Fourth Edition of the Alpha Architecture manual, DEC (now HP) Alpha has a Fault on Execute bit in page table entries with the OpenVMS, Tru64 UNIX, and Alpha Linux PALcode.[5]
The SPARC Reference MMU for Sun SPARC version 8 has permission values of Read Only, Read/Write, Read/Execute, and Read/Write/Execute in page table entries,[6] although not all SPARC processors have a SPARC Reference MMU.
A SPARC version 9 MMU may provide, but is not required to provide, any combination of read/write/execute permissions.[7] A Translation Table Entry in a Translation Storage Buffer in Oracle SPARC Architecture 2011, Draft D1.0.0 has separate Executable and Writable bits.[8]
Page table entries for IBM PowerPC's hashed page tables have a no-execute page bit.[9] Page table entries for radix-tree page tables in the Power ISA have separate permission bits granting read/write and execute access.[10]
Translation lookaside buffer (TLB) entries and page table entries in PA-RISC 1.1 and PA-RISC 2.0 support read-only, read/write, read/execute, and read/write/execute pages.[11][12]
TLB entries in Itanium support read-only, read/write, read/execute, and read/write/execute pages.[13]
As of the twelfth edition of the z/Architecture Principles of Operation, z/Architecture processors may support the Instruction-Execution Protection facility, which adds a bit in page table entries that controls whether instructions from a given region, segment, or page can be executed.[14]
APX and XN (execute never) bits have been added in VMSAv6 [Virtual Memory System Architecture]
Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
The NX bit (no-execute bit) is a processor feature that separates areas of a virtual address space (the memory layout a program uses) into sections for storing data or program instructions. An operating system supporting the NX bit can mark certain areas of the virtual address space as non-executable, preventing the processor from running any code stored there. This technique, known as executable-space protection or Write XOR Execute, protects computers from malicious software that attempts to insert harmful code into another program’s data storage area and execute it, such as in a buffer overflow attack. The term "NX bit" was introduced by Advanced Micro Devices (AMD) as a marketing term. Intel markets this feature as the XD bit (execute disable), while the MIPS architecture refers to it as the XI bit (execute inhibit). In the ARM architecture, introduced in ARMv6, it is known as XN (execute never). The term NX bit is often used broadly to describe similar executable-space protection technologies in other processors.
In computer science, execute in place (XIP) is a method of executing programs directly from long-term storage rather than copying it into RAM. It is an extension of using shared memory to reduce the total amount of memory required. Its general effect is that the program text consumes no writable memory, saving it for dynamic data, and that all instances of the program are run from a single copy. For this to work, several criteria have to be met: The storage must provide a similar interface to the CPU as regular memory (or an adaptive layer must be present). This interface must provide sufficiently fast read operations with a random access pattern. The file system, if one is used, needs to expose appropriate mapping functions. The program must either be linked to be aware of the address the storage appears at in the system or be position-independent. The program must not modify data within the loaded image. The storage requirements are usually met by using NOR flash memory or EEPROM, which can be byte-addressed for read operations, although it is a bit slower than normal system RAM in most setups.
Execute is the debut album of So Solid Crew members Oxide & Neutrino, released on 28 May 2001. It features the Casualty sampling number 1 single "Bound 4 da Reload (Casualty)" and the Prodigy cover "No Good 4 Me". The song "Devil's Nightmare" was also featured on the Lara Croft: Tomb Raider soundtrack.
In the United States, capital punishment (also known as the death penalty) is a legal penalty in 27 states (of which two, Oregon and Wyoming, have no inmates sentenced to death), throughout the country at the federal level, and in American Samoa. It is also a legal penalty for some military offenses. Capital punishment has been abolished in the other 23 states and in the federal capital, Washington, D.C. It is constitutionally permitted only for murder, with permissibility for use for crimes against the state not having been legally decided. Although it is a legal penalty in 27 states, only 21 of them have authority to execute death sentences, with the other 6 subject to moratoriums. There were no executions in the United States between 1967 and 1977. In 1972, the Supreme Court of the United States struck down capital punishment statutes in Furman v. Georgia, reducing all pending death sentences to life imprisonment. Subsequently, a majority of states enacted new death penalty statutes, and the court affirmed the legality of the practice in the 1976 case Gregg v. Georgia. Since then, more than 8,500 defendants have been sentenced to death; of these, more than 1,605 have been executed. Most executions are carried out by states. Since 1973, at least 200 people sentenced to death have been exonerated, about 2.2% of those sentenced. In 2019, the Trump administration's Department of Justice announced its plans to resume executions for federal crimes. On July 14, 2020, Daniel Lewis Lee became the first inmate executed by the federal government since 2003. Thirteen federal death row inmates were executed, all under Trump. The last and most recent federal execution during the first Trump administration was of Dustin Higgs, who was executed on January 16, 2021. On July 1, 2021, Attorney General Merrick Garland imposed a moratorium on federal executions. In April 2022, 2,414 people were on federal or state death row. On December 23, 2024, President Joe Biden commuted the sentences of 37 of the 40 individuals on federal civilian death row to life imprisonment without the possibility of parole; 3 people remain on federal death row. Pursuant to Executive Order 14164, signed by Donald Trump on January 20, 2025, the first day of his second term, then-Attorney General Pam Bondi issued a memorandum on February 5, 2025 that rescinded the Garland moratorium on federal executions. The memorandum also directed the Justice Department to strengthen the death penalty and seek its application by prosecutors whenever reasonable. Today, laws generally prohibit members of the general public from attending executions in the United States, though journalists and selected individuals may witness them. The last public execution in the U.S. took place in Kentucky on August 14, 1936, before a crowd of 20,000 people. This was followed by a period from 1936 to 1937 during which executions were semi-public, after which most states began requiring executions to be held privately. Timothy McVeigh's 2001 execution was viewed by over 200 people, mainly victims' families, via closed-circuit TV.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →The Greenwood District.
