Intel Corp., the world’s leading maker of microprocessors, chipsets and network components, Monday said it had been shipping central processing units with security capability called XD-bit for some time, while a number of retailers began to supply the chips to end-users.

“All the [microprocessor] parts with the “-J” designator have XD bit and have been shipping for several weeks now,” an Intel’s spokesman told X-bit labs.

Execute Disable bit a security feature that protects certain system memory data regions from insertion and execution of potentially harmful code, that is also referred as NX-bit and works only in conjunction with Windows XP operating systems that feature Service Pack 2.

Execute Disable bit allows the processor to classify areas in memory by where application code can execute and where it cannot. When a malicious worm attempts to insert code in the buffer, the processor disables code execution, preventing damage or worm propagation. To provide end-to-end no execute (NX) coverage, Intel already released XD-enabled chips for workstations, and other server products beginning in late Q3 2004. Desktop products are now shipping, with system availability in Q4 2004. Mobile processors will begin shipping in late Q4 2004, with system availability in Q1 2005.

“We did not make any official announcement on the XD bit enabled processors,” another Intel representative said.

Akiba PC Hotline web-site reports that the first batch of Intel Celeron D 340J, 335J, 330J and 325J has made it to the retail. End-users should get the revamped chips at approximately the same or slightly higher cost compared to versions without XD bit.

Intel said only Intel Celeron D chips in LGA775 packaging support XD bit technology, furthermore, BIOS and operating system of the system should support the tech to enable it.

Advanced Micro Devices, another leading maker of microprocessors, has been shipping AMD Opteron and AMD Athlon 64 central processing units with no execute bit (NX-bit) support since April and September, 2003, respectively. Intel first introduced its XD-enabled processor – the Itanium – in 2001.