Managing Memory. RAM on the Motherboard. Loses all data when PC is turned off (except data stored on CMOS chip) Two categories Static RAM (SRAM) Fast Used as a memory cache Dynamic RAM (DRAM) Slower; requires constant refreshing. DRAM. SRAM. Memory Technologies.
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RAM on the Motherboard • Loses all data when PC is turned off (except data stored on CMOS chip) • Two categories • Static RAM (SRAM) • Fast • Used as a memory cache • Dynamic RAM (DRAM) • Slower; requires constant refreshing
Dynamic RAM Technologies • Stored on DIMM, RIMM, or SIMM modules (plug directly into motherboard) • Differences among these modules: • Width of data path that each type accommodates • The way data moves from system bus to module
DRAM • SIMM technologies • Can use either EDO or FPM technology • DIMM technologies • Can use either BEDO (burst EDO) or synchronous RAM (SDRAM) • RIMM technologies • Each socket must be filled to maintain continuity
Error Checking and Parity • Parity • Error-checking procedure in which every byte has an even number of ones or an odd number of ones • Older method of testing integrity of bits • Stored in RAM or secondary medium • Sent over a communications device • Error-correcting code (ECC) • Current method of error checking that can detect and correct an error in a single bit
Other Memory Features • CAS (column access strobe) latency • RAS (row access strobe) latency • Both CAS and RAS refer to the number of clock cycles it takes to write or read a column or row of data
Memory Speeds: Factors to Consider • Speed of memory in ns, MHz, or PC rating • How much memory is installed • Memory technology used • CL rating • ECC/parity or non-ECC/nonparity
OS Memory Management • DOS and Windows 9x • Complicated; must deal with conventional, upper, and extended memory for backward compatibility • Windows NT/2000/NT • Eliminates complexity; memory is simply memory; all memory addresses are used the same way • Causes loss of backward compatibility
Windows 9x and DOS Utilities That Manage Memory • Himem.sys • Device driver for all memory above 640K • Emm386.exe • Contains software that loads device drivers and other programs into upper memory
How Windows 9x Manages Virtual Memory • Automates virtual memory management • Stores virtual memory in swap file and manages that memory for application programs • Controlled by the VMM (memory paging) • Symptoms of excessive memory paging • Very high CPU use • Very slow system response • Constant hard drive use
How Windows 2000/XP Manages Virtual Memory • Default size of paging file is set to 1.5 times amount of RAM installed • Guidelines for managing paging files • Set initial and maximum size of file to same value • Balance file size with disk space usage • Move paging file to a volume other than boot volume • Remember that memory dumps cannot be captured if the paging file is on a different physical disk from the OS