Fundamental of Computer Systems Memory Technologies 2024 PDF

Fundamental of Computer Systems Memory Technologies Prepared by: Gani Basheer Ahamed Modifications for 2024: Rajat Srivastava © Intel  Lecture overview Memory Units Types of Memory Cache and Virtual Memory Storage Technologies Disk Sto...

Fundamental of Computer Systems Memory Technologies Prepared by: Gani Basheer Ahamed Modifications for 2024: Rajat Srivastava © Intel  Lecture overview Memory Units Types of Memory Cache and Virtual Memory Storage Technologies Disk Storage Disk geometry and dynamics Connecting IO Devices Solid State Disk 2  Memory Unit The function of the memory unit is to store programs and data. Two classes - Primary storage and Secondary storage. Primary storage or Main Memory Programs are stored in the main memory while they are being executed. Example: RAM, ROM (As the CPU accesses both RAM & ROM) Secondary Storage Stores large amounts of data, instructions, and information more permanently than main memory. Example: Hard disk, CD, Flash memory 3  Types of Memory Main Memory Types Volatile Non-volatile RAM ROM 4  Memory Units Define bit / bits. ……8….. bits = 1 byte ……1024……bytes = 1kilo byte …1024…..kilo bytes = 1 Mega bytes Nibble = 4 bits Word = 16 bits = 2 bytes 5  Cache and Virtual Memory Concepts  Cache Memory: Cache memory is a supplementary memory system that temporarily stores frequently used instructions and data for quicker processing by the central processing unit (CPU) of a computer.  Virtual memory is a common technique used in a computer's operating system (OS). Virtual memory uses both hardware and software to enable a computer to compensate for physical memory shortages, temporarily transferring data from random access memory (RAM) to disk storage. 6  Storage Technologies Random Access Memory Random access memory (RAM)comes in two varieties— static and dynamic. Static RAM (SRAM) is faster and significantly more expensive than dynamic RAM (DRAM). SRAM is used for cache memories, both on and off the CPU chip. DRAM is used for the main memory plus the frame buffer of a graphics system. Typically, a desktop system will have no more than a few tens of megabytes of SRAM, but hundreds or thousands of megabytes of DRAM 7 Accessing Main Memory 8 Accessing Main Memory 9 Accessing Main Memory 10 Accessing Main Memory 11  Disk Storage Disks are constructed from platters. Each platter consists of two sides, or surfaces, that are coated with magnetic recording material. A rotating spindle in the center of the platter spins the platter at a fixed rotational rate, typically between 5,400 and 15,000 revolutions per minute (RPM). A disk will typically contain one or more of these platters encased in a sealed container. Figure 6.9(a) shows the geometry of a typical disk surface. Each surface consists of a collection of concentric rings called tracks. Each track is partitioned into a collection of sectors. Each sector contains an equal number of data bits (typically 512 bytes) encoded in the magnetic material on the sector. Sectors are separated by gaps where no data bits are stored. Gaps store formatting bits that identify sectors. 12 Disk Operation 13 Disk Geometry 14 Disk Capacity 15  Practice problem  What is the capacity of a disk with 3 platters, 15,000 cylinders, an average of 500 sectors per track, and 1,024 bytes per sector? 16  Disk Operation  Disks read and write bits stored on the magnetic surface using a read/write head connected to the end of an actuator arm, as shown in Figure 6.10(a). By moving the arm back and forth along its radial axis, the drive can position the head over any track on the surface. This mechanical motion is known as a seek. Once the head is positioned over the desired track, then, as each bit on the track passes underneath, the head can either sense the value of the bit (read the bit) or alter the value of the bit (write the bit). Disks with multiple platters have a separate read/write head for each surface, as shown in Figure 6.10(b). The heads are lined up vertically and move in unison. At any point in time, all heads are positioned on the same cylinder. 17  Connecting I/O Devices  Input/output (I/O) devices such as graphics cards, monitors, mice, keyboards, and disks are connected to the CPU and main memory using an I/O bus. Unlike the system bus and memory buses, which are CPU-specific, I/O buses are designed to be independent of the underlying CPU.  Three different types of devices attached to it. 1. Universal Serial Bus (USB) controller is a conduit for devices attached to a USB bus, which is a wildly popular standard for connecting a variety of peripheral I/O devices, including keyboards, mice, modems, digital cameras, game controllers, printers, external disk drives, and solid state disks. USB 3.0 buses have a maximum bandwidth of 625 MB/s. USB 3.1 buses have a maximum bandwidth of 1,250 MB/s. 18  Connecting I/O Devices  A graphics card (or adapter) contains hardware and software logic that is responsible for painting the pixels on the display monitor on behalf of the CPU.  A host bus adapter that connects one or more disks to the I/O bus using a communication protocol defined by a particular host bus interface. The two most popular such interfaces for disks are SCSI (pronounced “scuzzy”) and SATA (pronounced “sat-uh”). SCSI disks are typically faster and more expensive than SATA drives. A SCSI host bus adapter (often called a SCSI controller) can support multiple disk drives, as opposed to SATA adapters, which can only support one drive. 19 Bus Structure connecting CPU, memory and I/O 20  Data Access from Disk The first of these instructions sends a command word that tells the disk to initiate a read, along with other parameters such as whether to interrupt the CPU when the read is finished. The second instruction indicates the logical block number that should be read. The third instruction indicates the main memory address where the contents of the disk sector should be stored. 21 CPU Initiates Disk Read 22 Data transfer from Disk to Memory 23 Disk Controller notifies the CPU 24  Solid State Disk  A solid state disk (SSD) is a storage technology, based on flash memory, that in some situations is an attractive alternative to the conventional rotating disk. Figure 6.13 shows the basic idea. An SSD package plugs into a standard disk slot on the I/O bus (typically USB or SATA) and behaves like any other disk, processing requests from the CPU to read and write logical disk blocks.  An SSD package consists of one or more flash memory chips, which replace the mechanical drive in a conventional rotating disk, and a flash translation layer, which is a hardware/firmware device that plays the same role as a disk controller, translating requests for logical blocks into accesses of the underlying physical device 25 Solid State Disk 26  SSD operations  A flash memory consists of a sequence of B blocks, where each block consists of P pages. Typically, pages are 512 bytes to 4 KB in size, and a block consists of 32–128 pages, with total block sizes ranging from 16 KB to 512 KB. Data are read and written in units of pages.  A page can be written only after the entire block to which it belongs has been erased (typically, this means that all bits in the block are set to 1). However, once a block is erased, each page in the block can be written once with no further erasing. A block wears out after roughly 100,000 repeated writes. Once a block wears out, it can no longer be used.  Random writes are slower for two reasons. First, erasing a block takes a relatively long time, on the order of 1 ms, which is more than an order of magnitude. 27 Memory Hierarchy 28  Discussion Suggest further Reading topics: Characteristics of Random Access Memory. DRAM Structure and Operations. Core i7 Memory Module. Enhanced DRAMs Hard Disk Dynamics, Rotational latency, Access time, Transfer time etc. Any Questions ? 29