Abstract
The widening performance gap between processors and memory along with the growth of memory- intensive business applications are driving the need for better memory technologies for servers and workstations. Consequently, there are several memory technologies on the market at any given time. HP evaluates developing memory technologies in terms of price, performance, and backward compatibility and implements the most promising technologies in ProLiant servers. HP is committed to providing customers with the most reliable memory at the lowest possible cost.
This paper summarizes the evolution of memory technology and provides an overview of some the newest memory technologies that HP is evaluating for servers and workstations. The purpose is to allay some of the confusion about the performance and benefits of the dynamic random access memory (DRAM) technologies on the market.
Introduction
Processors use system memory to temporarily store the operating system, mission-critical applications, and the data they use and manipulate. Therefore, the performance of the applications and reliability of the data are intrinsically tied to the speed and bandwidth of the system memory. Over the years, these factors have driven the evolution of system memory from asynchronous DRAM technologies, such as Fast Page Mode (FPM) memory and Extended Data Out (EDO) memory, to high-bandwidth synchronous DRAM (SDRAM) technologies. Yet, system memory bandwidth has not kept pace with improvements in processor performance, thus creating a “performance gap.” Processor performance, which is often equated to the number of transistors in a chip, doubles every couple of years. On the other hand, memory bandwidth doubles roughly every three years. Therefore, if processor and memory performance continue to increase at these rates, the performance gap between them will widen.
Why is the processor-memory performance gap important? The processor is forced to idle while it waits for data from system memory. Thus, the performance gap prevents many applications from effectively using the full computing power of modern processors. In an attempt to narrow the performance gap, the industry vigorously pursues the development of new memory technologies. HP works with Joint Electronic Device Engineering Council (JEDEC) memory vendors and chipset developers during memory technology development to ensure that new memory products fulfill customer needs in regards to reliability, cost, and backward compatibility.
This paper describes the benefits and drawbacks regarding price, performance, and compatibility of DRAM technologies. Some descriptions are very technical. For readers who are not familiar with memory technology, the paper begins with a description of basic DRAM operation and terminology.
Basic DRAM operation
Before a computer can perform any useful task, it copies applications and data from the hard disk drive to the system memory. Computers use two types of system memory—cache memory and main memory. Cache memory consists of very fast static RAM (SRAM) and is usually integrated with the processor. Main memory consists of DRAM chips that can be packaged in a variety of ways on dual inline memory modules (DIMMs) for the notebook, desktop PC, and server markets.