Medium-term scheduler (used in time-sharing systems)

• manages processes waiting for resources
  • examples: waiting to be placed in main memory, waiting for i/o, or waiting to be placed in the ready list of the short tem scheduler.
• integrated with memory management routines (especially processes waiting for main memory)

Storage Hierarchy (Memory Hierarchy)

• cpu cache - memory located on the processor chip (VOLATILE)

• on-board cache - located on circuit board; fastest external memory available (VOLATILE)

• main memory - i.e., Simms, software managed (VOLATILE)

• secondary memory - i.e., hard drive (NON-VOLATILE)

• slow secondary memory - e.g., tapes, diskettes (NON-VOLATILE)

Volatile Storage

• volatile - contents lost if power is interrupted

  non-volatile - can withstand power failures and system crashes

Cache Memory

• source: FutureShop.ca web site
• A cache is a very fast block of memory that speeds up the performance of another device. Frequently used data are stored in the cache. The computer looks in the cache first to see if what it needs is there.
• Level 1 Cache is located directly inside the CPU itself, and stores frequently used data or commands. Although relatively small, Level 1 Cache has the most direct effect on overall performance.
• Level 2 Cache is located on the motherboard. It stores frequently used data from the computer's main memory (RAM). In Intel Pentium chips, Advanced Transfer Cache is an improved version of the Level 2 Cache, in which the cache memory operates at the same speed as the processor, which is as much as four times the speed of a standard Level 2 Cache

Pentium III Example (2001):

• primary or Level 1 (L1) cache - located in the Pentium III processor chip

  - 32Kb, with 16Kb for instructions and 16Kb for data

• integrated Level 2 (L2) cache (OR NEXT CHOICE) - extra memory located in the Pentium III processor chip

  
  - accessed by a 256-bit data bus - 8-way set associative

• discrete L2 cache called the Advanced Transfer Cache - EITHER THIS OR PREVIOUS CHOICE
  - connected to processor with a dedicated 64-bit cache bus
  - faster that cache-on-motherboard implementations

• main memory - SDRAMs

• secondary memory - hard drive

• slow secondary memory - tapes, diskettes

Current information

• components in a memory hierarchy
• Pentium example from 2001.

Cache memory

The Pentium III processor has two caches, called the primary or Level 1 ((L1) cache and the secondary or level 2 (L2) cache.

L1 Cache: Pentium 3 Cache is where the processor stores frequently accessed instructions or data for faster performance. The Pentium III processor incorporates a 32K Level 1 cache. This cache consists of 16K for instructions and 16K for data. This cache provides the highest information access speeds available. It is non-blocking, which means that _______.

L2 Cache: Working along with the L1 cache, the Pentium III processor has either a 512K unified, non-blocking, Level 2(L2) cache or an integrated 256K Advanced Transfer Cache. The integrated 256K L2 cache is located on-die and runs at the core frequency of the processor. The L2 cache is an area of high-speed memory that improves performance by reducing the average memory access time (source: Intel).

Main Memory

Prices on RAM (random access memory) vary depending on types and manufacturer. Current popular variety is Synchronized Dynamic Random Access Memory (SDRAM). SDRAM comes in increments of 64 MB, 128 MB, 256 MB and 512 MB. For an idea on prices check: