Memory & Storage: Crash Course Computer Science #19

Summary

This CrashCourse Computer Science episode explores the evolution of computer memory and storage. From volatile memory and its limitations to the advent of non-volatile storage, it covers the transition from punch cards to modern SSDs. The script delves into early technologies like Delay Line Memory and magnetic core memory, leading to innovations in magnetic tape, drums, and hard disks. It highlights the development of memory hierarchies and the exponential growth in storage capacity and accessibility, concluding with the rise of solid-state drives for faster, more efficient data handling.

Takeaways

• 💾 Computer memory is generally volatile, meaning data is lost when power is cut off, while storage is non-volatile and retains data even after power loss.
• 🔄 The traditional distinction between fast volatile memory and slow non-volatile storage is blurring with advancements in technology.
• 📚 Early computer storage included paper punch cards and punched paper tape, which were limited in capacity and speed.
• 📉 The largest known program stored on punch cards was the SAGE system, which required 62,500 punch cards, equivalent to about 5 megabytes today.
• 🔊 Delay Line Memory, invented by J. Presper Eckert, used liquid-filled tubes to store data as pressure waves, but was limited by sequential access.
• 🔗 Magnetic core memory, introduced in the 1950s, used magnetic 'donut' cores to store data and was a significant improvement over delay line memory.
• 💿 Magnetic tape, introduced with the UNIVAC computer, offered a new form of flexible, reel-based storage that could store a substantial amount of data.
• 🎛 Magnetic Drum Memory was a rotating cylinder with read/write heads used for data storage, but was eventually replaced by Hard Disk Drives.
• 🖲 The RAMAC 305, IBM's first computer with a disk drive, used 24-inch diameter disks to offer 5 megabytes of storage, highlighting the early stages of large-scale data storage.
• 💿 Optical storage, like CDs and DVDs, used physical divots to reflect light differently, encoding data optically rather than magnetically.
• 🛠 Solid State Drives (SSDs) are replacing traditional hard drives due to their lack of moving parts, offering faster access times and reliability.

Q & A

What is the primary difference between computer memory and storage?

Computer memory is volatile and loses data when power is lost, whereas storage is non-volatile and retains data even after power loss.

What was the earliest form of computer storage mentioned in the script?

The earliest form of computer storage was paper punch cards, which were later joined by punched paper tape.

How many bits of data could be stored on a single punch card according to the 1940s standard?

A single punch card could store a maximum of 960 bits of data based on the 80 columns and 12 rows standard.

What was the largest known program stored on punch cards and what was its approximate data size in megabytes?

The largest known program stored on punch cards was the US Military's SAGE, which required 62,500 punch cards, roughly equivalent to 5 megabytes of data.

What was the main drawback of using punch cards for computer storage?

Punch cards were slow, write-once (meaning data couldn't be easily changed), and they were less useful for memory where values might be needed for only a fraction of a second.

Can you explain how Delay Line Memory worked as described in the script?

Delay Line Memory worked by using a tube filled with a liquid like mercury. A speaker at one end would create a pressure wave that would travel to the other end and be detected by a microphone, converting it back into an electrical signal. The presence or absence of the pressure wave represented binary data.

What was the total memory capacity of EDVAC when it used 128 Delay Lines, each storing 352 bits?

The total memory capacity of EDVAC with 128 Delay Lines, each storing 352 bits, was 45,000 bits of memory.

Why was magnetic core memory a significant improvement over delay line memory?

Magnetic core memory allowed for random access, meaning any bit could be accessed at any time, unlike delay line memory which required waiting for the specific bit to come around in the loop.

What is a memory hierarchy and why is it used in computers?

A memory hierarchy is a system where computers use a combination of fast but expensive memory, medium-speed but less expensive memory, and slow but cheap memory. It balances cost and speed to optimize performance.

How did the cost of memory change from the early days of core memory to the present day?

The cost of memory has drastically decreased from millions of dollars per megabyte in the early days of core memory to mere cents by 2000, and fractions of a cent today.

What are the main advantages of Solid State Drives (SSDs) over traditional hard disk drives?

SSDs have no moving parts, which means they have faster access times (typically under 1/1000th of a second), are more durable, and produce less heat compared to traditional hard disk drives.