Introduction
A laptop, a cloud server, and the chip in a router are all computers, but each is built to optimize something different. That design goal decides what the hardware gives up, and what it gives up is often where vulnerabilities come from. This post compares the three classic classes of computers, personal computers, servers, and embedded computers (Patterson and Hennessy ch. 1), in one table, then explains each. Understanding a basic level of machine language and computer architecture is helpful when developing or attacking each type of computer. Specifically, understanding computer architecture can help developers disassemble code to determine poor coding practices which introduce vulnerabilities.
Development objectives summary
| Type | Development objective | Examples | Why it matters for security |
|---|---|---|---|
| Personal computers | Delivery of good performance to individual users at a low cost | Laptops, desktops | Runs lots of third-party software, so the attack surface is wide |
| Servers | Dependability | Web hosts, databases, cloud clusters | Downtime and data loss are the main costs; one compromise can affect many users |
| Embedded computer | Minimizing cost and power | TVs, routers, car and aircraft controllers | Tight budgets often mean fewer hardware protections and rare patches |
Newer editions of Patterson and Hennessy also describe a “post-PC era”: personal mobile devices (phones and tablets) have largely replaced the PC as the device people carry, and cloud computing runs on warehouse-scale computers, which are huge clusters of servers. The three classes below are still the clearest way to compare design goals, so the rest of this post covers each one.
Personal computers
PCs are computers designed for individual use. They are often used with a graphics display, a keyboard, and a mouse. The development objective of PC manufacturers is to deliver good performance to individual users at a low cost.
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Servers
Servers store, process, and manage data (ServerWatch). They often carry large workloads, such as a single complex application (e.g., a scientific application) or many small tasks (e.g., hosting, retrieving, and sending website files).
Server manufacturers focus on dependability because outages—a temporary suspension of operation—may cause users to lose access to critical data or services (American Heritage Dictionary).
The three most common causes are power supply failure (25%), cybercrime (22%) and accidental human error (22%) according to the Ponemon Institute.
When servers run or manage code, the server consumes energy, time, and money. Increased energy consumption and time translate to less financial gain for server users. Thus, developers may learn about basic low-level programming and computer architecture to improve the efficiency of their code, especially developers running code in the cloud, a global network of servers (Microsoft).
Embedded computers
Embedded computers are the largest class of computers by count. They represent one or more computers inside another device used for running one application or collection of software, for instance, a TV or dishwasher.
The development objective of embedded computers is to minimize cost and power. However, many also have a low failure tolerance since the results vary from “upsetting (when your new television crashes) to devastating (when the computer in a plane or cargo ship crashes)” (Patterson and Hennessy ch. 1).
Conclusion
This post was the first in my low-level series. Next, read Instruction Set Architectures, Computer Memory and Performance, and MIPS Assembly: Data, Registers, and Mimicking Scope, or browse all assembly posts. If you’re interested in security content, check out my offensive security work, like Offensive Security Attack Phases and Frameworks.
Citations
Patterson, David A., and John L. Hennessy. Computer Organization and Design MIPS Edition: The Hardware/Software Interface. Morgan Kaufmann, 2020.
